Field of the Invention
The present invention relates generally to the synthesis of a precise resistor, and more particularly to a monolithic resistor whose resistance is insensitive to the voltages across its two terminals.
Description of the Background Art
To produce a Hi-Fi sound in an audio application, the audio amplifier needs to produce a very low distortion signal. One major source of noise distortion is due to inherit resistance variations across the terminal voltages of a resistor. For a monolithic resistor, its resistance is sensitive to the values of the applied voltage across its two or more terminals. The resistance variations due to the applied voltage lead to significant distortions that can be detected by human ears.
A monolithic resistor is usually implemented by a poly-type resistor or a diffusion-type resistor. The material of a poly-type resistor is a polycrystalline silicon, which is a high purity, multi-crystalline form of silicon. A diffusion-type resistor is generally fabricated using one of the diffused or ion-implanted layers formed during the fabrication process or in some cases a combination of two layers. In CMOS, the diffused layer forming the source and drain of the MOS transistors can be used as a diffusion-type resistor. In silicon bipolar technology, the available diffused layers include base diffusion, emitter diffusion, active based region, and epitaxial layer. Unfortunately, these two types of resistors have large voltage-induced resistance variations no matter if they are lightly or heavily doped. The distortions caused cannot be ignored in Hi-Fi audio applications.